Recently, power supply apparatuses with two different voltage batteries have been installed in hybrid vehicles and engine vehicles. The power supply systems with two different voltage batteries will be referred to as “dual voltage apparatuses” hereinafter.
A dual voltage apparatus is normally equipped with a first power supply system including an engine-driven generator and a higher battery. The higher battery is chargeable by the engine-driven generator and has a first nominal voltage level. The dual voltage apparatus is normally equipped with a second power supply system including a lower battery with a second nominal voltage level lower than the first nominal voltage level. The second power supply system works to supply power to in-vehicle electrical loads.
The dual voltage apparatus is normally equipped with a power transfer unit electrically coupled to the first and second power supply systems. The power transfer unit is operative to convert a level of an output voltage of the first power supply system into a target level required for the second power supply system, and to transfer the output voltage, whose level has been converted, to the second power supply system.
Specifically, in the dual voltage apparatus, transfer of the output voltage from the first power supply system to the second power supply system via the power transfer unit allows level variation in a power supply voltage for the electrical loads to be reduced.
In the dual voltage apparatus, because power can be securely supplied to the electrical loads from the second power supply system, it is possible to change the state of charge (SOC) of the first higher battery when:
the higher battery voltage is output for driving torque generation; the higher battery is charged by regenerative electric power generated by the generator when braking; or the higher battery voltage is output for torque assist of the engine.
Especially, when the engine is not moving, power supply can be carried out from the higher battery to the electrical loads, making it possible to reduce level variation in an output voltage of the second power supply system.
Note that the electrical loads for example include lighting equipment, sound devices, and control units, which are susceptible to decrease in power supply voltage.
An example of the dual voltage apparatuses is disclosed in U.S. Patent Publication No. 6,583,602 corresponding to Japanese Unexamined Patent Publication No. 2002-345161, which was assigned to the same assignee.
In a dual voltage apparatus described above, power transfer can be carried out from the lower battery to the higher battery in order to make up for a shortage of the higher battery in capacity. As the higher battery, lithium secondary batteries, secondary batteries using a hydrogen storing alloy, and electric double layer capacitors can be used. As the lower battery, lead secondary batteries with high cost efficiency can be preferably used. Especially, the lithium secondary batteries have high charging capacity per weight, which can enhance fuel economy based on reduction in vehicle weight.
On the other hand, cooling systems for in-vehicle power devices through which a large amount of current is passed normally use a liquid or air cooling medium to be contacted onto a heatsink. For example, Japanese Unexamined Patent Publications No. H04-275492, H06-303704, and 2004-82940 disclose in-vehicle power devices equipped with corresponding air-cooling systems, respectively. Japanese Unexamined Patent Publication No. H09-126617 discloses an in-vehicle power device equipped with both air-cooling and liquid-cooling systems.
In addition, Japanese Unexamined Patent Publication No. 2004-39641 discloses a charging system with an air-cooling system in which airflow generated by a fan allows a battery and a charging device to be cooled.
Such liquid-cooling systems essentially include issues in which the more the system scale increases with the system structure complicated, the more the weight and a space required for installation of liquid-cooling systems increase. This makes it difficult to install such a liquid-cooling system in in-vehicle power devices.
Especially, in a liquid-cooling system, the heat transfer area between a heating element and a heat transfer medium can be reduced. However, it is difficult to reduce a heat transfer area of an indirect heat exchange unit required to dissipate heat absorbed by the heat transfer medium into the atmosphere.
For these reasons set forth above, in view of reduction in size and weight, an air-cooling system that subjects a heating element, a heat transfer medium stably contacted onto the heating element, or a heat pipe to cooling air can be preferably used. This air-cooling system has an advantage over a liquid-cooling system in reduction in size and weight, which makes it possible to increase the reliability of the air-cooling system.
Returning to the dual voltage apparatuses, as compared with power supply apparatuses with a single battery, the dual voltage apparatuses require, in addition to a first battery for supplying power to electrical loads, at least a second battery chargeable by a generator, and a power transfer unit for transferring power between the first and second batteries.
When install of the first and second batteries and the power transfer unit in a comparatively small-sized engine compartment located in front of a vehicle, they may be randomly arranged in the engine compartment, and thereafter, the first and second batteries and the power transfer unit may be electrically connected to each other by cables.
In this case, however, the cables may be routed for comparatively long distances in the engine compartment, causing the routing of the cables to be complicated.
The long and complicated routings of the cables may make it difficult to locate some of the cables away from high-temperature devices and/or rotating members located in the engine compartment. The former may result in malfunction in some of the cables, and the latter may interfere with the rotation of the rotating members.
The long and complicated routings of the cables may make it difficult to prevent some of the cables from being located close to the front (forward end) of the vehicle. This may cause brakes in some of the cables to be unavoidable in the event of a frontal crash.
In order to address the problems, the first battery and the power transfer unit may be installed in a trunk located at the rear of the vehicle. This way however may cause substantially identical problems due to the long and complicated routings of the cables by which the first and second batteries and the power transfer unit are connected to each other.
The long and complicated routings of the cables may increase:                power loss due to increase in resistance of the cables; and        weight of the dual voltage apparatus.        
In addition, there are various types of vehicles, such as engine vehicles driven by drive torque imparted by internal combustion engines, hybrid vehicles driven by drive torque and motor torque, and electric vehicle driven by motor torque. These various types of vehicles normally use a plurality of control units including inverters for motor control and/or DC to DC converters.
The control units installed in the various vehicles are operative to switch on and off power semiconductor devices that operate at high values of power, which may cause the power semiconductor devices, such as power transistors, to generate heat. For this reason, it is important to cool the power semiconductor devices installed in the control units.
Similarly, because in-vehicle batteries containing electric double layer capacitors repeatedly are frequently charged and discharged depending on variations in power required for in-vehicle electrical loads, they may internally generate a large amount of heat. Thus, it is also important to cool the in-vehicle batteries.
On the other hand, in the Unexamined Patent Publication No. 2004-39641, the air-cooling system, which is composed of a cooling fan, a motor that drives the cooling fan, and a motor controller that controls the motor, needs to be installed in the charging system integrated with the battery. This may cause the charging system to increase in size and weight, and cause the charging system structure to be complicated. In addition, the charging system structure may increase power consumption of the whole of the components (the cooling fan, motor, and motor controller), which may cause the battery to be exhausted.
This may not be avoided even if the cooling fan is separately arranged from the charging system, which is disclosed in the Publication No. 2004-39641.
As described above, installation of the air-cooling system in the charging system may cause the cost and/or the fuel consumption of the vehicle to deteriorate.